The present invention relates to a method of processing the surface of a specimen and an apparatus capable of performing this method; and, in particular, the invention relates to a method and apparatus suitable for plasma-etching the surface of a specimen on which semiconductor elements and the like are to be formed.
An apparatus for etching semiconductor elements, for example, an apparatus employing a co-called ECR (Electron Cyclotron Resonance) system, will be explained. This ECR system generates a plasma by exciting an inert gas in a vacuum container to which microwave energy and a magnetic field have been applied from the outside. The magnetic field causes electrons to move with a cyclotronic motion. The cyclotron frequency and the microwave frequency in resonance produce an environment in which a plasma can be generated efficiently. To accelerate plasma particles (ions) and cause them travel fast enough before striking a target in their path, a high-frequency voltage is applied to the target. A halogen gas, such as chlorine gas or fluorine gas, is used for generation of a plasma gas.
A high-precision type surface treating apparatus is disclosed in Japanese Non-examined Patent Publication No. 06-151360 (1994). This patent publication discloses that the intermittent on/off control of a high-frequency voltage applied to the target increases the selectivity of a surface substance (silicone) to be etched from the ground (oxide film) of a target and makes the etching rate less independent of conductor patterns. Further, in Japanese Non-examined Patent Publication No. 62-154734 (1987), there is disclosed a method of intermittently turning on and off a high-frequency voltage and etching slanted areas with a high-depositing etching gas. Furthermore, in Japanese Non-examined Patent Publication No. 60-50923 (1985), there is disclosed a method of intermittently turning on and off a high-frequency voltage according to the supply quantity of an etching gas to increase the anisotropy. Furthermore, U.S. Pat. No. 4,585,516 discloses a 3-electrode etching apparatus and a method of intermittently turning on and off a high-frequency voltage across two of such electrodes to assure a uniform etching speed over the whole wafer.